Utilization of mobile nodes such as wireless telephones, personal digital assistants (PDAs), handheld computers and other mobile communication devices is gaining popularity. The increased popularity is due in part to improved mobile access to real-time data, audio and video content enjoyed by users of such devices. This mobile networking capability allows relocation without disrupting real-time applications by automatically and non-interactively changing the mobile node's point of attachment as a mobile node relocates.
Mobile Internet protocol (IP) standards for transparently supporting changes in the point of attachment of mobile nodes include IP Mobility Support (Mobile IPv4) Network Working Group RFC 2002, C. Perkins (editor), October 1996 and Mobile Support in IPv6, IETF Mobile IP, David B. Johnson and Charles Perkins, Jul. 2, 2000. Among other things, these mobile IP standards support adjustments to the routing of messages as mobile nodes geographically relocate.
Typically, mobile nodes operate in a wireless network where points of attachment are provided by radio access points, or radio transceivers, that are geographically dispersed. The radio access points provide communication channels with mobile nodes as well as connectivity with wired networks via an access router. In addition, the radio access points perform handoffs of active communication channels when mobile nodes geographically relocate. In general, handoffs involve passing a communication channel that is currently in use from one radio access point that a mobile node is moving away from, to another geographically adjacent radio access point in closer proximity to the current location of the mobile node.
If geographically adjacent radio access points are associated with different access routers, and therefore different subnets, a handoff between such radio access points may also involve adjustments to the message routing. To perform handoffs that involve message routing adjustments, the mobile nodes need to be aware of the presence of the access routers associated with geographically adjacent radio access points. In the prior art, the current access router may indicate the presence of other access routers to the mobile node from a predetermined list of next candidate access routers. When different subnets are part of two different heterogeneous networks, however, the predetermined list may not include an access router associated with a geographically adjacent radio access point. Similarly, the predetermined list may be incomplete when two subnets within homogeneous networks are topologically distant.
One existing approach to overcome this problem is to manually configure each access router with a geographical neighborhood of other access routers. Such an approach, however, has disadvantages and in many cases may not be feasible. For instance, some of the geographically adjacent access routers may be under different administrative control, and thus, may not be informed of each other's presence. Even within the same administrative domain, the manual configuration approach demands precise network planning to determine the geographical coverage areas of different access routers.
The manual configuration approach may also prove labor intensive and inefficient where the access routers can be physically relocated or experience changes in coverage area. In these cases, the geographical scope of the coverage areas may need review and revision each time such changes occur. Relocation and coverage area changes are common in areas of increasingly heavy traffic where access routers may be temporarily and/or permanently introduced.
Another approach is based on special location information such as GPS (Global Positioning Satellite) systems. A GPS based system can provide physically adjacent candidate access routers and/or access points to current access points and/or mobile nodes. GPS, however, is not always available especially within buildings and other structures where satellite communication is difficult.